From the initial examination of Tuvix (in the episode of the same name), we learn that flowers had been fused into the new being at the genetic level:
EMH: I'm also picking up traces of a third genetic pattern. It appears to be plant-based.
TUVIX: The orchids. We had collected several dozen samples of orchids. They were in our sample containers when we beamed up.
EMH: Well, they're part of your genetic structure now. But they don't appear to be affecting your biochemistry.
When Tuvix is disintegrated at the end of the episode, we see Neelix and Tuvok reemerge on the bio-bed but not the orchids:
What happened to the plant DNA?